Preheat oven to 325F. Grease muffin tin or line with muffin liners.
In a large bowl, sift flour, baking powder and salt.
Warm milk, vanilla and butter in microwave until butter is melted. Set aside to cool a little.
In a large heatproof bowl, combine whole eggs, yolks and sugar. Using a handheld electric mixer, beat on high speed until foamy for a minute. Set bowl over a pan of barely simmering water. Beat on high speed until sugar is dissolved and mixture is warm. Remove bowl from heat, continue whisking until mixture becomes thick and pale in colour.
Gently but thoroughly fold egg mixture into the flour mixture in 3 batches. Stir 1/2 cup batter into the milk mixture to thicken, then fold milk mixture into the remaining batter until just combined.
Divide batter evenly among prepared muffin cups. Transfer muffin tin to oven and bake for 18 to 20 minutes, until the edges are light golden brown. Transfer muffin tin to a wire rack and let cupcakes cool completely.
Mix all espresso syrup ingredients. Let the syrup cool to room temperature. Poke holes with a fork on top of each cupcake before brushing the syrup on top. Repeat until all the syrup is used. Allow cupcakes to absorb liquid for 30 minutes.
To prepare frosting, in a bowl of a standing mixer with a whisk attachment, beat heavy cream until it holds stiff peaks. Transfer to another bowl. Whisk mascarpone and powdered sugar until smooth. Gently fold in the whipped cream until completely incorporated.
Frost the cupcakes with the mascarpone. Dust with cocoa powder. Topped each cupcake with an espresso macaron if you prefer.